The present invention relates to an apparatus for continuous slurry displacement transfer and, more particularly, to an apparatus of the kind mentioned above capable of detecting any failure in the sequence beforehand and representing or informing the content of the failure.
U.S. Pat. No. 3,556,682, for example, discloses an apparatus for slurry displacement transfer comprising a plurality of vessels arranged in parallel, a low-pressure slurry pump for charging into the vessels with slurry consisting of water and solid matters and a high-pressure driving liquid pump for displacing the slurry from the vessels to an outlet pipe, wherein the position of respective float members positioned at the boundary between the slurry and the driving liquid in each vessel is detected by outside detectors which produce signals for opening and closing valves in inlet and outlet pipes for the driving liquid and valves in inlet and outlet pipes for the slurry.
In the actual operation of slurry displacement transfer apparatus, it is extremely difficult to make the discharging flow rate Q1 strictly equal to the charging flow rate Q2 of the slurry. Even if flow rate control could be perfectly performed for respective vessels, it is quite difficult in terms of accumulated errors of meters to maintain upward and downward movement of the float members within the vessels in the same manner over a long period of time.
As a measure for overcoming this problem, it has been proposed to provide a change-over means capable of effecting a switching of the operation mode between a first mode in which the charging flow rate Q2 of the slurry due to upward movement of the float members is slightly smaller than the discharging flow rate Q1 of the slurry due to downward movement of the float members (e.g. Q2=0.95 Q1) and a second mode in which the former is slightly greater than the latter (e.g. Q2=1.05 Q1).
In the operation of the slurry displacement transfer apparatus in the manner as described above, a detector for detecting lower limit position of the float member causes closing of a valve An in the driving liquid inlet pipe and opening of a valve An+1 in the succeeding vessel at the same time, and a detector for detecting upper limit position of the float member causes closing of a valve Cn in the driving liquid outlet pipe and opening of a valve Cn+1 in the outlet pipe for the succeeding vessel, thereby to prevent cut-off operation of the pump and reverse-flow of the slurry.
If the apparatus is operated in the condition of Q2=1.05 Q1, the float member reaches its upper limit position at the level of the detector comparatively in a shorter period of time since the flow rate Q2 is larger than the flow rate Q1. In other words, the period of time during which the float member is in the lower limit position is reduced while the period of time during which it is in the upper limit position is increased. The operation mode is switched to the first mode, i.e. to the mode of Q2=0.95 Q1 immediately before the sequence becomes inoperative as a result of the reduction in the period of time during which the float member is in the lower limit position. This switching is repeated during a continuous operation of the apparatus, so that the flow rates Q2, Q1 can be equal to each other over a long period of time.
In the conventional slurry displacement transfer apparatus as described above, the operator or engineer must inspect the control panel to seek for the cause of a failure when the sequence is out of order.
When the slurry is not discharged through the outlet pipe, it is presumed that, although a change-over valve A is about to be opened, a valve D in the slurry outlet pipe is in the opened state with the float having not reached yet the upper limit position. Thus, in most cases, failures are attributable to a leak in the valves. When the sequence becomes out of order as described above, it is necessary to suspend the operation of the apparatus, even when the circumstance requires to keep up with the operation for a short period of 10 to 30 minutes. It is also necessary to find out the faulty devices (valve).